For nearly a century Friedel-Crafts reactions were carried out in solution using AlCl.sub.3 and related Lewis acid halide type catalysts. These reactions, some of which gained very significant industrial application, such as the ethylation of benzene, and the isomerization of hydrocarbons, are all well recognized to involve the formation of highly colored complex layers (so called "red oils"). These complexes are now understood to contain significant concentrations of carbocationic tetrachloroaluminate salts and tie-up large amounts of the catalyst in its catalytically inactive coordinated anion form. Further, decomposition of the complex layers necessitates additional steps and generally results in the loss of the catalyst.
The realization of the nature of the Friedel-Crafts reactions and their catalyst resulted in an understanding of the generalized acid catalyzed characteristics of these reactions, and allowed the use of a large variety of not only Lewis, but of Bronsted type catalyst systems. The use of supported solid acid catalysts, allowing catalytic heterogeneous reactions, was, until very recently, of limited scope. They utilized only in specific instances, such as in the preparation of cumene via propylation of benzene with propylene, using catalysts of the supported solid phosphoric acid type. Similar reaction conditions for the preparation of ethylbenzene from benzene and ethylene were found less satisfactory. Ethylation was observed to take place only at higher temperatures, and even more significantly, the transethylation of benzene with di- or polyethylbenzenes, inevitably formed in the reactions, is not satisfactorily realized under heterogeneous catalytic conditions.
Friedel-Crafts isomerization of hydrocarbons, such as of alkanes to highly branched isomeric mixtures or the isomerization of dialkylbenzenes, such as xylenes, was also until now predominantly carried out with liquid Friedel-Crafts catalyst systems such as AlBr.sub.3, AlCl.sub.3, HFBF.sub.3 etc.
Nonbonded electron-pair containing systems such as aldehydes, ketones, and the like, when formed in Friedel-Crafts reactions, coordinate equimolar amounts of AlCl.sub.3, or related catalysts and thus generally necessitate the use of molar excess of "catalyst", as well as decomposition of stable catalyst-product complexes. These and related conditions limit the industrial and practical use of Friedel-Crafts reactions compared with other catalytic systems, such as metal and organometallic catalyzed transformation reactions, isomerization, and the like.
It is on this basis, consequently, that there is substantial practical significance in this invention to modify the usual Friedel-Crafts type reactions in a way which can be described on the basic principle to bind the catalyst to a suitable solid surface or carrier which would then allow the use of these systems as effective solid acid catalysts.